X-ray diagnostic apparatus for preparing x-ray exposures including an automatic illuminating device and automatic adjustment of the exposure voltage

ABSTRACT

An automatically illuminatable X-ray diagnostic apparatus which, in comparison with the state of the technology is considerably simplified with respect to its operation by avoiding the need for adjustment of the X-ray tube voltage. The X-ray tube voltage therein automatically adjusts itself in conformance with a preselected contrast. The X-ray tube voltage is automatically lowered by means of adjusting means for commencing an exposure within a short period as compared with the shortest exposure time, from a maximum initial value corresponding to the largest patient bulkiness, and in which the adjusting means is controllable by a comparator element having introduced at one input thereof a differential quotient of a proportional value of the dosage load measured behind the patient in the direction of the X-rays pursuant to the X-ray tube voltage at the instantaneous X-ray tube voltage as the actual value, while at the other input thereof there is provided a reference value signal corresponding to the desired contrast and which conveys a signal to the adjusting means for maintaining the X-ray tube voltage as soon as both input signals are equal. The reference value signal herein is a percentage figure of a differential quotient of the dosage load behind the patient, and corresponding to the desired contrast, pursuant to the X-ray tube voltage at a relative reference X-ray tube voltage of proportional value.

United States Patent [1 1 Franke [451 Oct. 7, 1975 [75] Inventor:

[73] Assignee: Siemens Aktiengesellschait,

Erlangen, Germany 221 Filed: Feb. 4, 1974 211 Appl. No.: 439,612

Kurt Franke, Erlangen, Germany Primary Examiner-Davis L. WillisAttorney, Agent, or Firm-Waters, Schwartz & Nissen 5 7 ABSTRACT Anautomatically illuminatable X-ray diagnostic apparatus which, incomparison with the state of the technology is considerably simplifiedwith respect to its operation by avoiding the need for adjustment of theX-ray tube voltage. The X-ray tube voltage therein automatically adjustsitself in conformance with a presev lected contrast. The X-ray tubevoltage is automatically lowered by means of adjusting means forcommencing an exposure within a short period as compared with theshortest exposure time, from a maximum initial value corresponding tothe largest patient bulkiness, and in which the adjusting means iscontrollable by a comparator element having introduced at one inputthereof a differential quotient of a proportional value of the dosageload measured behind the patient in the direction of the X-rays pursuantto the X-ray tube voltage at the instantaneous X-ray tube voltage as theactual value, while at the other input thereof there is provided areference value signal corresponding to the desired contrast and whichconveys a signal to the adjusting meansfor maintaining the X-ray tubevoltage as soon as both input signals are equal. The reference valuesignal herein is a percentage figure of a differential quotient of thedosage load behind the patient, and corresponding to the desiredcontrast, pursuant to the X-ray tube voltage at a relative referenceX-ray tube voltage of proportional value.

6 Claims, 5 Drawing Figures U.S. Patent Oct. 7,1975 Sheet 1 of23,911,273

DL AS FUNCTION OF UR DL AT U A d (DL AS FUNCTION OF U URMAX d(DL ASFUNCTION O U d UR US. Patent Oct. 7,1975 Sheet 2 of2 3,911,273

function Sample P' generate and 22 A circqii FIELD OF THE INvENTIoN Thepresent invention relates to an X-ray diagnostic apparatus for thepreparation of X-ray exposures, including an automatic exposure timerdevice for the automatic switching off of the X-ray tube upon apredetermined ray dosage being received by the X-ray film, and includingautomatic adjusting means for the X-ray tube voltage.

DISCUSSION OF THE PRIOR ART In known X-ray diagnostic apparatus havingautomatic exposure timer devices, adjustment must be provided for theX-ray tube voltage. The switching off of the X-ray tube, in effect, thecompletion of an exposure, is obtained the required X-ray dosagepredetermined for optimum film darkening has been imparted to the film.The X-ray tube voltage must, in that instance, be adjusted in dependenceupon the object being penetrated by the rays, so as to provide anoptimum picture contrast. The adjustment of the X-ray tube voltage iseffected by means of tables, orbased on the experience of the examiningperson.

Through German Pat. No. 1,227,570 there has become known automaticallyilluminated X-ray diagnostic apparatus having adjusting means for theX-ray tube voltage and the' X-ray tube current, including an overloadprotective device for indicating and adjusting the limiting time independence upon the preadjusted X-ray tube load by means of the X-rayload nomograph or computing chart, as well as through an X-ray dosageload measuring device located behind the object being X-rayed. In thisX-ray diagnostic apparatus there is provided a control arrangement,which upon an adjustment of the overload protective device, located onthe basis of the preadjusted value of the existent tube load presentlylies at a predetermined breakage point below the limiting load of theX-ray tube, then raises the X-ray tube voltage during the first exposurephase until it attains the limiting load limit of a permissiblemagnitude, when the predetermined dosage load measurement commenced withexposure initiation indicates that the required X-ray dosage for thedesired film darkening cannot be attained with the preadjusted dosageload within the settime limit. In this X-ray diagnostic apparatus thereis achieved an automatic correlation between the X-ray tube voltage andthe bulk of the patient. Also attainable is a predetermined degree ofautomation of the adjustment of the X-ray tube voltage. However, theinitial value of the X-ray tube voltage must always be selected inconformance with the body portion or organ which is to be X-rayed.Additionally, for the exposure of a predetermined body portion or organthere are only two different X-ray tube voltages available, so thatcorrelation to the varied constitutions of patients is only roughlyobtained. Consequently, also this X-ray diagnostic apparatus, not alwayscan there be obtained an optimum illumination time at the lowestpossible ray load on the patient and at an optimum image contrast.

SUMMARY OF THE INVENTION It is, accordingly, an object of the presentinvention to provide an X-ray diagnostic apparatus of the typedescribed, in effect, an automatically illuminatable X-ray diagnosticapparatus which, in comparison with the state of the technology isconsiderably simplified with respect to its operation, inasmuch as thereis no longer a need for adjustment of the X-ray tube voltage. The X-raytube voltage therein automatically adjusts itself in conformance with apreselected contrast.

The foregoing task is inventively solved in that the X-ray tube voltageis automatically lowered by means of adjusting means for commencing anexposure within a short period as compared with the shortest exposuretime, from a maximum initial value corresponding to the largest patientbulkiness, and in which the adjusting means is controllable by acomparator element having introduced at one input thereof a differentialquotient of a proportional value of the dosage load behind the patientpursuant to the X-ray tube voltage at the instantaneous X-ray tubevoltage as the actual value, while at the other input thereof there isprovided a reference value signal corresponding to the desired contrastand which conveys a signal to the adjusting means for maintaining theX-ray tube voltage as soon as both input signals are equal. Thereference value signal herein is a percentage figure of a differentialquotient of the dosage load behind the patient, and corresponding to thedesired contrast, pursuant to the X-ray tube voltage at a relative X-raytube voltage of proportional value. In the inventive X-ray diagnosticapparatus there is no longer a requirement for the adjustment of theX-ray tube voltage. It is merely necessary to select the desired imagecontrast. This selection sequence, however, is only to be relativelyseldomly required. Within the scope of the invention, the desired imagecontrast may also be fixedly adjusted when a contrast variation is notconsidered to be needed. The operation of the inventive X-ray diagnosticapparatus thus becomes extremely simple, inasmuch as practically noexposure data need be selected. Consequently, a fully automaticoperation of the apparatus becomes possible.

Within the framework of the invention there may be, on the one sideconveyed to a differentiating element, for the formation of a valueproportional to a differential quotient of the dosage quantity behindthe patient in the direction of teh X-rays according to the X-ray tubevoltage, a voltage of the automatic exposure timer device which isproportional to the instantaneous dosage, and, on the other side,avoltage which is proportional to the instantaneous X-ray tube voltage.The automatic exposure timer device herein is employed for thegeneration of switching off signal for the X-ray tube, as well as foradjustment of the X-ray tube voltage. Consequently, there is providedthereby an extremely simple construction.

A particularly simple construction is achieved when the reduction of theX-ray tube voltage for commencement of the exposure from the maximuminitial value thereof is effected in a time-proportional manner. In thatinstance it is not required to actually determine the X-ray tubevoltage. It is much more adequate that the differentiating elementtimewise differentiates a voltage from the automatic exposure timerdevice proportional to the instantaneous dosage.

A further embodiment of the invention consists of in that the X-ray tubevoltage, through there is imparted the required differential quotientfor the formation of the reference value, is also switched over independence upon the selected contrast, and wherein the maximum initialvalue of the X-ray tube voltage for initiating the exposure lies only asmall amount above the present X-ray tube voltage effective for thedifferential quotient.

BRIEF DESCRIPTION OF THE DRAWINGS Further advantages of the presentinvention may be now ascertained from the following detailed descriptionof an exemplary embodiment thereof, taken in conjunction with theaccompanying drawings, in which:

FIG. 1 is a graphical representation of the relationship of the dosageload at various X-ray tube voltages with respect to the dosage load at apredetermined maximum X-ray tube voltage for various patient bulks;

FIG. 2 illustrates differential quotients of the dosage load behind thepatient (DL) according to the X-ray tube voltage in dependence upon theX-ray tube voltage, as obtained from the curves in FIG. 1, regulated forthese differential quotients at a maximum X-ray voltage (U "M" forvarious patient bulks;

FIG. 3 illustrates a circuit diagram for an X-ray diagnostic apparatusaccording to the present invention;

FIG. 4 graphically illustrates a sequence for the X-ray tube voltage inthe X-ray diagnostic apparatus of FIG. 3; and I FIG. 5 shows circuitdetails of the circuit diagram of FIG. 3.

DETAILED DESCRIPTION Referring now to the drawing, in FIG. 1 the X-raytube voltage is designated by U The curve 1 relates to a thin patient,whereas curve 4 relates to a bulky patient. The curves 2 and 3correspondingly relate to intermediate values of patient bulks.

The image contrast K of an X-ray exposure remains, not-withstandingvariations in the bulk D of a patient, approximately constant when theX-ray tube voltage U is adjusted in a manner in which the quotient Qremains constant from the differential quotient of the dosage quantitybehind the patient pursuant to the X-ray tube voltage at the location U(exposure voltage) and the differential quotient of the dosage quantitybehind the patient pursuant the X-ray tube voltage at the location of asuitable X-ray tube voltage U which is larger than U In short form:

K f(d). in the event U U,, wherein U, is such,

that

The sequence or graph of the quotient Q in dependence upon the X-raytube voltage U is illustrated in FIG. 2. The curves 5 through 8 hereincorrespond to curves 1 through 4 in FIG. 1. In FIG. 2 there is shown aline 9 which defines a particular preselected contrast. From FIG. 2 itmay be ascertained that in order to obtain a contrast according to line9 for patients represented by curves 1 and 5, there is required an X-raytube" voltage of approximately kv, while for patients represented bycurves 4 and 8, there is required an X-ray tube voltage of approximatelykv. From FIG. 2 it is ascertainable that completely determinate X-raytube voltage U, f(d) belongs to each patient constitution, and whichthere is obtained a predetermined contrast. v

The invention recognizes that the image contrast, as well as the givenquotient of the differential quotients, are dependent upon the patientbulk and the exposure voltage, and that this dependence of the imagecontrast and the given quotient from the patient bulk may be compensatedfor in that the exposure voltage follows the patients bulk in adetermined function U =f(d), and wherein this function U f (d) is thesame for the image contrast and the quotient Q, so that it is onlynecessary to maintain the X-ray tube voltage at that value whichprovides a preselected quotient, in order to thereby concurrently alsoachieve the associated image contrast.

An X-ray diagnostic apparatus which operates in accordance with thisprinciple is illustrated in FIG. 3 of the drawings. The X-ray diagnosticapparatus according to FIG. 3 includes a rotary or three-phase highvoltage transformer 10 having a split secondary side. Two high voltagerectifiers l1 and 12 supply an X-ray tube 13 through two conduits l4 and15 which are positioned in the high voltage circuit. The conduits 14 and15 have control arrangements or amplifers l6 and 17 associatedtherewith, by means of which the anodecathode resistance of the conduitsl4 and 15, and thereby the voltage reduction of the conduits l4 and 15,becomes adjustable. Through the intermediary of control arrangements oramplifiers l6 and 17, the X-ray voltage tube thus may be adjusted.

The control of the control arrangements or amplifiers l6 and 17 iseffected through a function generator 18 which has an input 19, andwhich maintains to final value throughwhich it controls the controlarrangements or amplifiers l6 and 17 as soon as a signal is generated atits input, in effect, in the conduit 19.

The conduit 19 is, at the other side thereof, connected to a comparisoncircuit 20 which receives at a portion comprising a resistance 21, as areference value the output voltage of a sample and hold circuit 22, andas an actual value the timewise differentiated output voltage of a doserate meter 25, through a condensor 23 and resistance 24. The dose ratemeter 25 is connected with a suitable ray detector 26 which is locatedbehind the patient 27 in the direction of the X-rays and, in FIG. 3, infront of (in practice also possibly in back of) the X-ray film 28.

The output voltage of the dose rate meter 25, which has been timewisedifferentiated by means of condensor 23 and resistance 24, is alsoconveyed to the circuit 22. The differentiated output voltage of thedose rate meter 25 which, at a particular moment after commencement ofthe exposure, is present at the resistance 24, is sensed by the sampleand hold 22, supplied and then maintained at the resistance 21 for aslong until a signal appears in the conduit 19.

The output signal of the dose rate meter 25 is, in addition to thedifferential components 23, 24, conveyed toward an integrator 29, andthe integrator result to a cut-off amplifier 30 which has a referencevalue input 1 high voltage transformer for the switching off of theX-ray tube 13.

At the output of the dose rate meter 25 there is formed a voltage whichis proportional to the measured dosage quantity in back of the patient27in the direction of the X-rays. The resistance 24 is small incomparison with the fraction T in which T,, T (see FIG. 4 for that time,within which the X-ray tube voltage, for commencing the exposure at asuitably high value, reaches its correct value U,, and in which C is theca pacity of condensor 23. The voltage at the resistant 24 is defined bythe following equation:

in which I(* is a constant. In order to obtain a linear dropping off ofthe X-ray tube voltage, the function generator 18 is programmed in amanner so that this linear reduction is effected for'as long as thevoltage at the resistance 24 is larger than the voltage atthe tap-offfor resistance 21, in effect meaning, as long as no signal istransmitted from the comparison circuit to the conduit 19.

If dt with respect to the relationship for the X-ray tube voltage U isintroduced in the relationship for the voltage U,, at the resistance 24,then the following equation is obtained for the voltage U In thisequation the differential quotient of the dosage quantity is obtainedpursuant to the X-ray tube voltage. Based on the prior assumption thatthe X-ray tube voltage drops off linearly with time, then the voltageU,, in the embodiment of FIG. 3 may be utilized for obtaining thequotient Q, as follows:

The operation ofthe X-ray diagnostic apparatus of FIG. 3 is as follows,having reference to FIG. 4:

The X-ray tube voltage U after commencement of the X-ray exposure, jumpsto a suitable maximum value U This is retained until time point T andthen drops linearly. 1

At the resistance 24 there appears a voltage impulse in conformance withthe sudden occurrence of the dosage. After the voltage impulse hasreduced prusuant to T and the voltage U,,- is now proportional to thedifferential quotient d (DL)/d U then U,,- (U,,-) at U is sensed andsupplied or energized.

(U,,) at U then appears at the output of circuit or unit 22. Through theintermediary of resistance 21, a predetermined portion (percentage)corresponding to the desired image contrast is transmitted to thecomparison circuit 20, as represented by:

Q (UK) at mmm mit Q 1 AT T, or respectively, at U U the followingpertains:

R) I (z/(DLJ) R) lunu For U there results for various patient bulks,from exposure to exposure, always a different value, and namely theX-ray tube voltage which independently of the patients bulk alwaysconstantly provides the same contrast. At the time point T there isaccordingly maintained the X-ray tube voltage at the value U 1 and theX-ray exposure is'preparedat the voltage U up to the time point T atwhich the cut-off amplifier 30 terminates the exposure. After the timepoint T the X-ray tube voltage drops exponentially toward zero. Theslope or degree of drop-off of the X-ray tube voltage for initiating theexposure is so selected, that the dosage which is produced in the time Tis also at the lowest occurring X-ray tube voltage small in comparisonwith the dosage between the time T and the minimum employed exposuretime T so that during the largest portion exposure time there providedat the X-ray tube an X-ray tube voltage corresponding to the optimumcontrast. i

In summation, it may be readily ascertained that in the X-ray diagnosticapparatus according to FIG. 3 there is no requirement for an adjustmentof the X-ray tube voltage. Since the X-ray tube current may also berigidly programmed pursuant to the loading nomograph of the X-ray tube,the operation and manipulation of this X-ray diagnostic apparatus isconsiderably simplified, inasmuch as practically no exposure data needbeadjusted; The desired contrast may singly be adjusted'for a pluralityofexposures at the resistance 21, and thecorrelation with the employedX-ray film similarly 'fillows for a plurality of exposures at a singleinstance through generation of a corresponding signal at the input 31 ofthe cut-off amplifier 30. The X-ray diagnostic apparatus according toFIG. 3 consequently is completely automatedly exposed, and in which theadjusting sequence for the X-ray tube voltage is incorporated in theautomation thereof.

The embodiment according to FIG. 3 is particularly simple since theX-ray tube voltage drops off linearly with time, and consequently noparticular evaluation of the X-ray tube voltage changes need be effectedthrough corresponding measuring elements. Within the framework or scopeof the invention, the reduction or dropping off of the X-ray tubevoltage may also follow in conformance with another function. If thisfunction is fixedly programmed in the function generator 18, then alsoin this instance no measurement of the particular actual value of theX-ray tube voltage change is required, but merely the differentiationcannot be effected by means of the RC-element 23, 24, and a moresuitable differentiator must be introduced. Within the scope of theinvention it is also possible, to ascertain the dosage quantity change,as well as the X-ray tube voltage change be ascertained throughcorresponding measuring elements, and to form the differential quotientby means of a differentiating element. It is always important for theinvention that a signal be transmitted to the comparison circuit 20which is proportional to the differential quotient of the dosagequantity pursuant to the X-ray tube voltage, and in which the signal iscompared with a signal proportional to the reference value of thecontrast corresponding percentage value of a differential quotient ofthe dosage quantity pursuant to the X-ray tube voltage at a referenceX-ray tube voltage, and upon the balancing of the signals the X-ray tubevoltage is maintained.

The construction of the function generator 18 is described in greaterparticularity in FIG. 5 of the drawings. From FIG. 5 it is ascertainedthat the function generator 18 includes a condensor 33 which isdischargeable through a discharge resistance 34, as well as through arelay contact 35. The relay contact 35 is actuatable by means of a relay36 which is controlled by the cut-off amplifier 30. The switching-in ofthe discharge resistance 34 at the condensor 33 is effected through acircuit switch 37 and a relay contact 38, whose relay 39 is controlledby the signal in the conduit 19.

Prior to commencing an exposure, the exposure switch 37 is opened andthe condensor 33 is charged. in order to initate an exposure, the switch37 is closed. The condensor 33 discharges approximately linearly throughresistance 34 up to the time point T Since the X-ray tube voltagecorresponds to the condensor voltage, the X-ray tube voltage also dropslinearly up to time point 7}, pursuant to FIG. 4. The control voltagefor the conduits or triodes l4 and namely corresponds with the voltagein the conduit 40, which is amplified through the control amplifiers l6and 17.

At the time point 7' the voltage U, is attained in the X-ray tube, andthe comparison circuit transmits a signal to conduit 19, which causesthe relay 39 to open its contact 38 and interrupt the discharge ofcondensor 33. The condensor voltage thereby remains constant up to timepoint 7}, whereby the X-ray tube voltage also maintains the value U, upto time point T,. At time point T, there is effected the termination ofthe exposure by means of the output signal of the cut-off amplifier 30,which causes the excitation of relay 36. Relay 36 closes its contact 35and completely discharges condensor 33. The condensor voltage, andtherewith the X-ray tube voltage, extend herewith from time point T, on,pursuant to the graph in FIG. 4, until reaching zero value. Prior toinitiating a new exposure, the relay 36 is again de-energized so thatthe contact 35 is opened. Furthermore, the exposure switch 37 is againopened prior to initiating an exposure, and for the making of a newexposure, closed again. The above-described sequences are then repeated.

While there has been shown what is considered to be the preferredembodiment of the invention, it will be obvious that modifications maybe made which come within the scope of the disclosure of thespecification.

What is claimed is:

1. In an X-ray diagnostic apparatus having an X-ray tube for the makingof X-ray exposures of a patient; including an automatic exposure timermeans for automatically switching off the X-ray tube upon an X-ray filmbeing subject to a predetermined dosage of rays; and means forautomatically adjusting the voltage of the X-ray tube, the improvementcomprising; said voltage adjusting means being adapted to automaticallylower the X-ray tube voltage at the initiation of each exposure during asmall time interval in comparison with the shortest exposure time ofsaid apparatus from a maximum initial value, equal for all examinations,and based on a largest patient bulk; and comparison circuit meansoperatively connected to said voltage adjusting means and adapted tocontrol the latter, said comparison circuit having a first inputreceiving a signal as an actual value proportionate to a differentialquotient of the X-ray dosage quantity measured behind the patient in thedirection of the X-rays pursuant to the X-ray tube voltage, and a secondinput receiving a reference value signal corresponding to a desiredimage contrast; and means transmitting a signal from the output of saidcomparison circuit means to said voltage adjusting means for maintainingthe X-ray tube voltage constant upon said first and second input signalsbeing equal.

2. An apparatus as claimed in claim 1, said reference value signal atthe second input of said comparison circuit means being incorrespondence with the desired image contrast, a percentage of a signalproportional to the differential quotient of the dosage quantitymeasured behind the patient in the direction of the X-rays pursuant toan X-ray tube voltage.

3. An apparatus as claimed in claim 1, comprising differentiating meansfor generating a signal conforming to the formation of change in thedosage quantity measured behind the patient in the direction of the X-rays; and dose rate meter means connected to said differentiating meansfor measuring voltage proportional to the dosage quantity.

4. An apparatus claimed in claim 3, said differentiating means having anoutput signal adapted to generate one of the input signals of saidcomparison circuit means.

5. An apparatus as claimed in claim 1, comprising means for fixedlyprogramming the function of the reducing rate of the X-ray tube voltage.

6. An apparatus as claimed in claim 4, said programming means linearlyreducing said X-ray tube voltage as a function of time.

1. In an X-ray diagnostic apparatus having an X-ray tube for the making of X-ray exposures of a patient; including an automatic exposure timer means for automatically switching off the X-ray tube upon an X-ray film being subject to a predetermined dosage of rays; and means for automatically adjusting the voltage of the X-ray tube, the improvement comprising; said voltage adjusting means being adapted to automatically lower the X-ray tube voltage at the initiation of each exposure during a small time interval in comparison with the shortest exposure time of said apparatus from a maximum initial value, equal for all examinations, and based on a largest patient bulk; and comparison circuit means operatively connected to said voltage adjusting means and adapted to control the latter, said comparison circuit having a first input receiving a signal as an actual value proportionate to a differential quotient of the X-ray dosage quantity measured behind the patient in the direction of the X-rays pursuant to the X-ray tube voltage, and a second input receiving a reference value signal corresponding to a desired image contrast; and means transmitting a signal from the output of said comparison circuit means to said voltage adjusting means for maintaining the X-ray tube voltage constant upon said first and second input signals being equal.
 2. An apparatus as claimed in claim 1, said reference value signal at the second input of said comparison circuit means being in correspondence with the desired image contrast, a percentage of a signal proportional to the differential quotient of the dosage quantity measured behind the patient in the direction of the X-rays pursuant to an X-ray tube voltage.
 3. An apparatus as claimed in claim 1, comprising differentiating means for generating a signal conforming to the formation of change in the dosage quantity measured behind the patient in the direction of the X-rays; and dose rate meter means connected to said differentiating means for measuring voltage proportional to the dosage quantity.
 4. An apparatus as claimed in claim 3, said differentiating means having an output signal adapted to generate one of the input signals of said comparison circuit means.
 5. An apparatus as claimed in claim 1, comprising means for fixedly programming the function of the reducing rate of the X-ray tube voltage.
 6. An apparatus as claimed in claim 4, said programming means linearly reducing said X-ray tube voltage as a function of time. 